It is known to provide radiant heaters for heating glass ceramic hobs with a temperature limiting device. This leads to the glass ceramic being protected against overheating and the resulting thermal stress breaks. Such a temperature limiting device can either be an electromechanical temperature controller in the form of a so-called rod controller, which brings about the switching off of the heating device of the glass ceramic hob on reaching a preset switching point at a temperature considered to be critical. It is alternatively possible to provide electronic temperature limiting devices with a temperature sensor in the form of a temperature-dependent resistor on the heating device and also an associated electronic limiting unit, particularly a control unit.
The advantage of the second possibility with the temperature sensors is that in addition to the protective function further functions can be implemented, such as for example, a hot display indicator for the glass ceramic hob with adjustable release point, temperature-regulated hotplates or automatic cooking controls, etc. For the temperature sensor itself, use is frequently made of temperature-dependent metal film resistors, particularly platinum resistors, for example so-called PT1000 resistor-temperature sensors. However, these are expensive, and also their maximum use temperature of approximately 750° C. is not adequately high for safe operation, particularly for use on glass ceramic hobs with radiant heaters. Thus, known temperature sensors of this type cannot be placed in the direct action area of radiant heaters and must instead be located in the marginal area or under shielding, etc., but in certain circumstances doing so results in inaccurate measurements.